Method for interior-space/exterior-space detection of a response transmitter which communicates in wire-free fashion with a base station, and a communications system

ABSTRACT

Method for interior-space/exterior-space detection of a response transmitter which communicates in wire-free fashion with a base station, and communications system A communications system contains a base station ( 8 ) with a transmitter/receiver unit ( 10 ) for communication signals and a transmitter unit ( 14 ) for location interrogation signals; a response transmitter ( 20 ) with a transmitter/receiver unit ( 22 ) for the communication signals, and a receiver unit ( 26 ) for location interrogation signals. An interior space ( 2 ) which is located within the operating range of the communications system has walls ( 4 ) which are impermeable to one frequency range. The communication signals are transmitted and received in a frequency range to which the walls 4 are permeable. The location interrogation signals are transmitted in the frequency range to which the walls are impermeable.

[0001] The invention relates to a method forinterior-space/exterior-space detection of a response transmitter whichcommunicates in wire-free fashion with a base station, and acommunications system.

[0002] Communications systems are known which have a base station whichcontains a transmitter/receiver unit, and a response transmitter which,with a signal containing an item of code information, transmits aresponse signal in response to an interrogation signal, which responsesignal is received by the base station and evaluated with respect to thecode information in order to identify the response transmitter.

[0003] In such a system known from EP 0 153 613 B1, the responsetransmitter contains a strip of magnetostrictive, ferromagnetic materialwhich resonates mechanically at a preselected frequency within afrequency band. This response-transmitter specific resonance is detectedby the base station as code information, with the result that when thecode information corresponds to a previously stored code informationitem an access system, for example, is enabled. The particular advantagefor a user of such a communications system lies in the fact that merelycarrying the response transmitter is sufficient to provide proof of theperson's access authorization. In the keyless access system which isknown from EP 0 153 613 B1 and which is used, for example, in a motorvehicle, a plurality of interrogation zones are defined by connecting aplurality of transmitter/receiver antennas to the base station, saidantennas being arranged at predetermined points on the vehicle, forexample in the vicinity of the driver's door and front seat passenger'sdoor and being used to emit short-range interrogation signals, to whosereception the response transmitter responds. It is also possible toarrange such an antenna within the trunk so that it is detected whetherthe response transmitter has been left in the trunk, and given apositive detection the trunk is, for example, automatically preventedfrom being locked. The known keyless access system contains additionalproximity sensors so that it is activated to emit an interrogationsignal only if a person approaches a proximity sensor, for example.

[0004] A desirable, additional functionality of such a communicationssystem consists in the fact that it is possible to detect whether theresponse transmitter is located inside or outside a space, in which casethe communication between base station and response transmitter will bemaintained irrespective of the location of the response transmitter,provided that the response transmitter is located in the transmitterrange of the base station. In this way, it is possible to carry outenabling measures or control measures which depend on the location ofthe response transmitter or of a person carrying the responsetransmitter, these being for example, special authorizations forcarrying out safety-relevant functions, as soon as it is ensured thatthe response transmitter is located in an interior space.

[0005] The invention is based on the object of implementing, in acommunications system with at least one base station and at least oneresponse transmitter, the functionality of detecting whether theresponse transmitter is located inside or outside a space.

[0006] The method defined in claim 1 provides a means of achieving theabovementioned object.

[0007] An interior space in conjunction with which the method accordingto the invention can be applied is, for example, a space which isenclosed by electrical conductors. Such a space can be a space within abuilding, for example a space which is critical for safety, or theinterior of a motor vehicle, etc. Depending on the construction of theelectrical conductors, electromagnetic waves above a predeterminedfrequency are allowed to pass through, essentially without attenuation,through the walls into the interior space. On the other hand, at largewavelengths or very low frequencies, the incoming waves or fields arenot let through the walls owing to the influence of the electricalconductors. Communication between the base station and the responsetransmitter in a frequency range which is let through by the walls canthus be carried out irrespective of whether the base station and theresponse transmitter are located inside or outside the interior space.On the other hand, communication in a frequency range to which the wallsare impermeable can take place only if the base station and the responsetransmitter are located on the same side of the walls of the interiorspace. By making expedient use of both frequency ranges for thecommunication it is thus possible for the response transmitter and thebase station to communicate with one another continuously, but it isstill possible to determine whether they are located on different sidesof the walls of an interior space.

[0008] The subclaims 2 to 5 are concerned with advantageous ways ofimplementing the method according to the invention.

[0009] Claim 6 is concerned with the basic design of a communicationsystem for achieving the object of the invention.

[0010] This communication system is advantageously developed with thefeatures of claims 7 and 8.

[0011] According to claim 9, the communications system is suitable inparticular for use within anti-theft system or access control system ofa motor vehicle.

[0012] The invention is explained in more detail below by way of exampleand with reference to schematic drawings, in which:

[0013]FIG. 1 shows a block circuit diagram of a communications systemaccording to the invention, and

[0014]FIG. 2 shows a flowchart explaining the method of operation of thecommunications system.

[0015] According to FIG. 1, an interior space 2 is surrounded by walls 4which are indicated by dashed lines and which contain electricalconductors 6, for example in the form of a lattice or in the form offlat components, as in the example of a motor vehicle.

[0016] In the example illustrated, a base station 8 is equipped, insidethe interior space 2, with a transmitter/receiver unit 22 with atransmitter/receiver antenna 12 via which communication signals aretransmitted and received. Furthermore, the base station 8 has atransmitter unit 14 for local interrogation signals, which transmitterunit 14 is connected to a transmitter antenna 16 located in the interiorspace 2, and a transmitter antenna 18 located in the exterior space.

[0017] The base station 8 contains further units (not illustrated) forgenerating the transmitted signals and for evaluating the receivedsignals, as well as a control unit, preferably provided with amicroprocessor, for controlling the operation.

[0018] The design and function of the individual elements or modules ofthe base unit are known per se and therefore not explained.

[0019] Furthermore, the system includes a response transmitter 20 with atransmitter/receiver unit 22 for communication signals, whichtransmitter/receiver unit 22 has a transmitter/receiver antenna 24, anda receiver unit 26 with a receiver antenna 28 for local interrogationsignals.

[0020] In a way similar to the base station 8, the response transmitter20 contains assemblies for generating these transmission/receptionsignals, for storing code information, for evaluating the receivedsignals and for controlling the entire operation, and the design of saidassemblies is known per se and is therefore not explained. The basicdesign of the response transmitter 20 can be similar, with the exceptionof the additionally provided receiver unit 26, to that of the datacarrier, known per se, or response transmitter of keyless access controlsystems of motor vehicles.

[0021] For the walls 4 of the interior space 2 there is a criticalwavelength λ_(c) which is dependent essentially on the distance betweenthe electrical conductors 6 and above which electromagnetic waves do notpenetrate the walls owing to the shielding effect of the electricalconductors 6. For the wavelengths λ_(K) which are used in communicationsignals, and for the wavelengths λ_(o) which are used for localinterrogation signals, the following applies: λ_(K)<λ_(C)<λ_(O) .Accordingly, the operating range of a local interrogation signal orlocal detection signal is restricted to the region outside or inside theinterior space 2 depending on whether the transmissions occur outside orinside the interior space, while the operating range of thecommunication signals covers the exterior and the interior space. Thepower with which the communication signals are transmitted, and thesensitivity of the associated receiving devices, are advantageouslyselected in such a way that the operating range is greater than theexternal dimensions of the interior space 2 and smaller than theoperating range of a local interrogation signal. In FIG. 1, acommunication signal 30 is represented throughout as a bidirectionalsignal. A local interrogation signal 32 is represented as aunidirectional signal by means of dashed lines.

[0022] In an extreme case, the frequency of a local interrogation signalmay be virtually zero, i.e. a static electrical field can be excited.

[0023] The method of operation of the system described will be explainedbelow with reference to an example of an interrogation strategyaccording to FIG. 2.

[0024] It will be assumed that the base station 2 outputs acommunications interrogation signal KAFS periodically or controlled as afunction of events. If one of a plurality of possible responsetransmitters is located in the operating range of the base station 2 orinside its transmitting range, this response transmitter responds instep 42 with a communications response signal KATS which contains itsidentifier. This response signal KATS is received by the base station 8in step 44 and the identifier is checked in step 46. Given a check witha positive result (step 48), the system knows that there is anauthorized response transmitter located in its area.

[0025] In order to initiate a specific action, the system must know,inter alia, whether the response transmitter, or a response transmitter,is located inside or outside the interior space 2. For example, thevehicle is only allowed to be locked if a response transmitter islocated outside the interior space, or the motor is only allowed to bestarted if a response transmitter is located inside the interior spaceetc. It will be assumed in the present example that in step 50 it isdetermined that a local detection is necessary because it has to bedetected, for example for a locking operation, whether a responsetransmitter is located outside the interior space or the vehicle. Thebase station 2 then transmits, in step 52, a communication signal AKwith the content that a location interrogation signal is transmitted ata time t₁. The response transmitter activates, in step 54 at the timet₁, its receiver unit 26 for the reception of the local interrogationsignal. At the time t₁, the base station 8 transmits the localinterrogation signal OAFS via the antenna 18 located outside theinterior space 2. After the time t₁, the response transmitter 20 informsthe base station 8, in a communications response signal in step 60,whether or not it has received the local interrogation signal in step58.

[0026] If the local interrogation signal OAFS has been received in step58, it is possible to conclude that the response transmitter 2 islocated outside the interior space 2 and the vehicle can be locked(steps 62, 64).

[0027] If no local interrogation signal was received, it may beexpedient to make additional positive checks as to whether the responsetransmitter is located in the interior of the vehicle in order to makesure that the non-reception of the local interrogation signal is not dueto an error in the response transmitter. To do this, steps 72 to 84which are similar to steps 52 to 64 are run, with the single differencethat the local interrogation signal OAFS is transmitted by the antenna16 located within the interior space 2 at a time t₂. This time istransmitted to the response transmitter 20, as described above, by meansof a communication signal in step 72. The response transmitter thenswitches its receiver unit 26 to the active state in step 74 at the timet₂. The response transmitter 20 subsequently informs the base station 8,in step 80, whether or not the response interrogation signal has beenreceived.

[0028] If the response transmitter 20 has not received a localinterrogation signal at the time t₁ and has received a localinterrogation signal at the time t₂, it is reliably determined that theresponse transmitter is located inside the interior 2 (step 84).

[0029] The time period between t₁ and t₂ is advantageously selected tobe small in order to ensure that the position of the responsetransmitter has changed only slightly during the interrogations.

[0030] The system described above and the interrogation strategy can bemodified in diverse ways.

[0031] The determination of the location advantageously takes place insuch a way that the space is interrogated first, and the localinterrogation signal is transmitted via that antenna which is assignedto that space in which the signal transmitter must be located for anaction to be enabled.

[0032] Alternatively, the local interrogation signal can be generated bythe response transmitter and evaluated in the base station which thenhas two reception antennas.

[0033] The base station and/or the response transmitter may be designedin such a way that in each case the reception of a local interrogationsignal which is transmitted in the frequency range to which the wallsare impermeable automatically triggers a response signal which istransmitted in the other frequency range. In this way, that part of thebidirectional communication which otherwise takes place exclusively inthe frequency range to which the wall 4 is permeable and triggers anactivity of a part (data carrier or base station) which receives a localinterrogation signal, takes place by means of the local interrogationsignal which is used unidirectionally.

[0034] In order to shorten the reaction time, the communication signalsand the local interrogation signal can be generated simultaneouslybecause they can be identified unambiguously owing to their differentfrequencies. Furthermore, the communication signals within acommunications frequency channel can be transmitted with a specificbandwidth. The same applies to the local interrogation signals.

[0035] If local interrogation signals with different features are usedinside the interior space and outside the interior space, identicaltimes can be selected for the times t₁ and t₂.

[0036] The antennas and the transmitter/receiver units for the differentfrequency ranges can be combined, insofar as is technically appropriateand expedient, within the base unit and the response transmitter.

[0037] The fact that the bidirectional communication takes place at thehigher frequency meets the need to operate with a high Baud rate on thecommunications channel. On the other hand, by means of thelower-frequency local interrogation signal it is possible to operatewith a high field strength so that the local interrogation signal can beused, for example, to activate or wake up the signal transmitter for acommunication. It is also advantageous here that with the low-frequencyinterrogation signal the entire interior space is reliably covered andinterrogated when an interior space interrogation occurs. Of course, theinterrogation strategy or the bidirectional communication may beappropriately modified if the signal transmitter is only activated by alocal interrogation signal.

1. A method for interior-space/exterior-space detection of a responsetransmitter (20) which communicates in wire-free fashion with a basestation (8), walls (4) of an interior space (2) being impermeable to afrequency range, in which method two frequency ranges are used for thecommunication between the base station (8) and the response transmitter(20), the walls (4) of the interior space (2) being permeable to a firstfrequency range and impermeable to a second frequency range.
 2. Themethod as claimed in claim 1, the communication from the responsetransmitter (20) to the base station (8) taking place in the firstfrequency range.
 3. The method as claimed in claim 1 or 2, the basestation (8) transmitting a communication signal in the first frequencyrange and a location interrogation signal in the second frequency range.4. The method as claimed in one of claims 1 to 3, the base station (8)transmitting location interrogation signals selectively from inside oroutside the interior space (2).
 5. The method as claimed in claims 3 or4, the response transmitter (20) being woken up using the locationinterrogation signal.
 6. A communications system containing a basestation (8) with a transmitter/receiver unit (10) for communicationsignals and a transmitter unit (14) for location interrogation signals,a response transmitter (20) with a transmitter/receiver unit (22) forthe communication signals and a receiver unit (26) for locationinterrogation signals, and an interior space (2) whose walls (4) areimpermeable to one frequency range, the communication signals beingtransmitted and received in a frequency range to which the walls arepermeable and the location interrogation signals being transmitted in afrequency range to which the walls are impermeable.
 7. Thecommunications system as claimed in claim 6, the base station (8) havinga transmitter antenna (12) outside the interior space and a transmitterantenna (16) inside the interior space.
 8. The communications system asclaimed in claim 6 or 7, the response transmitter (20) containing codedata which, for its identification, it transmits collectively inresponse to a communications interrogation signal.
 9. The communicationssystem as claimed in claim 8, the communications system being acomponent of an anti-theft system of a motor vehicle, the base station(8) being in the motor vehicle and the response transmitter (20) beingcarried by a person.